The present invention relates to transponders, and, more particularly, to the structure of transponders or "tags" which comprise, as a minimum, a substrate, an antenna arranged on the substrate and a signal processing chip (preferably a surface acoustic wave or "SAW" device) coupled to the antenna.
Transponder tags of the aforementioned type receive an interrogating signal from a remote transmitter; process that interrogating signal to generate a reply signal; and transmit the reply signal to a receiver and decoder which receives the transponder generated reply signal and decodes that reply signal for further use. Each transponder is provided with unique encoded information that is incorporated into the reply signal. Such transponders are generally referred to as "passive" because they do not carry a self-contained power source, such as a battery, that must be replaced from time to time. Transponders of this type are described in U.S. Pat. No. 4,725,841 for "System For Interrogating A Passive Transponder Carrying Phase-Encoded Information"; U.S. Pat. No. 5,095,240 for "Inductively Coupled SAW Device And Method For Making The Same"; U.S. Pat. No. 4,737,789, for "Inductive Antenna Coupling for a Surface Acoustic Wave Transponder", and U.S. Pat. No. 4,951,057 for "Inductive Input/Output Coupling for a Surface Acoustic Wave Device". These transponders are used, for example, as personnel identification tags and for vehicle identification on highways and parking lots.
The U.S. patent application Ser. No. 08/636,903 (now allowed) discloses a layered structure for a transponder tag of this type which is simple to manufacture and assemble. The entire disclosure of this U.S. patent application Ser. No. 08/636,903 is incorporated herein by reference. The transponder tag, as disclosed therein, sandwiches an antenna between a cover sheet and substrate and provides an opening through the cover sheet to receive a signal processing chip (e.g., a SAW device) disposed beneath a cap so as to be coupled to the antenna, either directly or indirectly.
The signal processor chip is adhesively secured beneath the cap which is, in turn, secured to the top the cover sheet. The cover is fabricated with a rectangular opening that receives the signal processing chip.
According to a further aspect of this prior disclosure, an antenna is provided on a first surface of a substrate and sandwiched between the substrate and a cover. The rectangular opening which extends through the cover receives the signal processing chip adhesively secured beneath the cap so that the chip is spaced from, but is inductively coupled to the antenna.
This layered transponder structure requires that the substrate at the base of the transponder tag be relatively rigid. Otherwise, the substrate may be pressed upward during normal use and come in contact with the active area of the signal processing chip.